This invention relates to a device for checking positional accuracy and, more particularly, to a device for checking the relations among a plurality of positions.
There are cases where a plurality of parts must be mounted on an object in a precise positional relation to one another. For example, in a video tape recorder (VTR) two magnetic heads must be mounted on a rotary disk such that they are exactly 180 degrees out of phase from each other. If the two magnetic heads are not exactly 180 degrees out of phase from each other, mistracking will occur and the image reproduced from the video tape by the magnetic heads will be blurred. For this reason, it is important in the assembly of the VTR to check whether the two magnetic heads are exactly in the specified positional relation to each other.
Hitherto, the checking of the positional relation between the magnetic heads has been done using a pair of microscopes arranged exactly 180 degrees out of phase from each other on the rotary disk. More particularly, the positional relation between the two heads is checked by checking whether the head gaps of the magnetic heads, as seen in an enlarged view through the respective microscopes, are in register with the center of field of the microscopes. This method, however, requires a great deal of time and skill for positioning the pair of microscopes exactly 180 degrees out of phase, and the probability of error is very high. Further, the focus adjustment and observation of the parts must be done through the eyepiece of the microscopes, and the inspection criteria thus vary from one observer to the next, which leads to inconsistencies in the checking results. Still further, when the disk is rotating, a check to determine whether the heads are out of phase or not cannot be made via this method. Generally, the relative positions of the heads change according to stop and moving conditions of the disk, due to members such as bearings. As to the VTR heads, it is important to check their relative positions when the disk is in a moving condition, since this condition resembles the actual manner of use.